1. Field of the Invention
The present invention relates generally to a method of determining subterranean formation fracture orientation, and more particularly, but not by way of limitation, to a method of determining fracture orientation wherein a fracture is created in a formation and a location orientated core containing a portion of the fracture is removed therefrom.
2. Description of the Prior Art
In the production of fluids such as oil, gas and water from a subterranean rock formation penetrated by a wellbore, a commonly used technique for stimulating the production of fluids from the formation is to create and extend fractures therein. Most often, the fractures are created by applying hydraulic pressure on the formation from the wellbore. That is, a fluid is pumped through the wellbore and into the formation to be fractured at a rate such that the resultant hydraulic force exerted on the formation causes one or more fractures to be created therein. The fractures are extended by continued pumping, and the fractures are usually propped open after being formed and extended so that fluids contained in the formation readily flow through the fractures into the wellbore. Fracturing techniques are also used in formations penetrated by injection and production wells which are utilized for carrying out enhanced production procedures therein, e.g., waterflood and other similar recovery procedures, as well as in other oilfield applications.
Subterranean rock formations are usually bounded by formations formed of dissimilar rock materials. Because of this, in carrying out fracture stimulation procedures in a formation from which it is desired to produce fluids, it is often necessary and always desirable to know the direction of the least in situ principal stress in each formation, i.e., the direction in which fractures will extend in the formation, as well as the relative levels of the least in situ principal stresses in the formations. For example, when the formation containing desired fluids is bounded by one or more formations containing undesired fluids, if it is known that the formation containing desired fluids has the lowest least in situ principal stress level, then fractures can be created and extended in that formation without fear of fracturing the formations containing undesired fluids. If the converse situation exists and is known, a production stimulation procedure other than one involving fracturing can be utilized.
In a given field containing a reservoir of desired fluids, it is desirable to know the orientation of fractures induced in formations containing the fluids so that the drilling of wellbores into the formations and the production of fluids therefrom can be optimized and maximum production obtained. In other operations such as in carrying out enhanced production procedures and solution mining procedures where communication between wellbores is required, a knowledge of the orientation of induced fractures is essential to bringing about such communication.
By the present invention a method of determining induced fracture orientation, i.e., the direction of the least in situ principal stress, in one or more subterranean formations is provided. The fracture orientation information obtained can be utilized to determine if fracture techniques should be carried out in the formations, where other wellbores should be drilled, which of two or more formations has the lowest least in situ principal stress level and consequently will fracture first, and the like.